Blower Ducting Set Up

[snook91901]

I'm the proud new owner of a '63 Columbia 29 with an uninstalled A4. I am trying to plan my ducting for the engine compartment blower but I have a bit of a problem.
I'm not sure if the typical set up with an intake under the engine in the engine compartment leading to a blower fan and then a rear facing cowl is the wisest set up for my boat. The problem is that the bilge is open to the engine compartment. Therefore any gasoline fumes will collect in the bottom of the bilge instead of the engine compartment. This is potentially dangerous IMO as the typical intake set up will not evacuate the fumes and any spark in the bilge, say from a faulty automatic bilge pump, could ignite them.

So should I
(1) run my intake down into the bilge
(2) have an intake both under the engine and in the bilge with a T connector
(3) do my best to seal up the connection
???

I'm hoping to avoid option 3 because several connection run through this passage, but I realize it may still be the best option.

ps this is my first posting to the forum so let me say thank you to everyone at MMI for keeping so many A4's alive.

[snook91901]

Blower Ducting Set Up

I'm the proud new owner of '63 Columbia 29 with an unistalled (and neglected- see my introduction post) A4 and I have run into a bit of a problem planning the ducting for my blower.

I'm afraid the typical set up with the intake under the engine leading to a blower fan and aft facing exhaust cowl will not work with my boat because the engine compartment is open to the bilge beneath. IMO this represents a serious safety problem because the gasoline vapors will run into the bilge compartment and will not be vented by the blower. Additionally, a bilge full of fumes may meet an ignition source due to a faulty automatic bilge pump.

So what should I do?
(1) run the intake down into the bilge
(2) install a T and have two intakes, one in the bilge and one in the engine compartment
(3) seal off the engine compartment from the bilge
(4) something else entirely

I'd not prefer option 3 if at all possible because a bilge pump hose runs up towards the transom through this opening.

ps. this is my first post to the forum so let me say thank you to everybody at MMI for keeping so many A4s alive.

[Loki9]

Welcome to the forum.

Aren't the engine room and the bilge always connected? If not, then what happens to water that gets into the engine room? Anyway, the two are connected on my boat.

The duct to the blower in my engine room runs to the lowest point, just in front of the flywheel cover. There's also a second fresh air inlet duct that terminates on the other side of the motor and somewhat above the first duct.

I think this setup does a good job of evacuating fumes from around the engine and it probably gets most of them out of the bilge (it always passes the sniff test). The engine is the most likely source of ignition, and I don't worry about the bilge pump because it only comes on when it's underwater.

[JOHN COOKSON]

Pervention

Two items to consider along this line:
Always turn the fuel supply off at the tank and run a bit of fuel out of the line before shutting the engine off.
Leave the engine area open as possible at all times.
If you are concerned about fumes in the bilge use your personal fume detector. (nose)

If you put the intake tube in the bilge it will float on top of any water in the bilge. If you anchor it down it could end up under water. Either way not the best situation.

Most boats I've seen have an instillation like Loki9 described.

And welcome to the forum.

TRUE GRIT

[lat 64]

Welcome,
I think the "tee" option could work, but mine is just same as Loki9's setup.
If you put in a tee, then you might have to balance it a bit. I don't see any real technical hurdles though.

I have a Columbia too. A '68 36. Not really similar boats but family.
I read that the mold for the early 29 was taken off a wooden boat and the lines in the hull were left in the new mold. I found the story somewhere out there in internet land. The boat next to mine in Homer Harbor is a '66 Islander 29. Does yours have lines like a wooden boat?
With all the genetic pooling of boat designers and plants back then I can imagine they might be very similar.

Russ

[Carl-T705]

You are correct, if the vapors can seek the lowest point (bilge) that is where the blower needs to draw from. If you simply want to exhaust heat and fumes from the engine, when running, which is a great idea , put a second blower in, drawing from the top side of the engine to do this. Since bilge pumps are generally submerged when they are needed to run I wouldn't be to concerned about it igniting fumes. BUT If you are on the boat, you should turn on the blower before turning anything spark producing on. Good Luck

[ILikeRust]

Interesting point - to me, anyhow, because my boats' setup is the same - the engine sits a fiberglass bed, which sits directly above the deepest part of the bilge.

I would lead the exhaust duct down into the bilge, if this causes you concern.

Another thing to consider, which I have partly setup, is to purchase at least one, and preferably two, Nicro solar "day/night" vent fans. Set one to pull air into the boat, and the other to draw air out. Install the "inbound" one forward in the boat - e.g., over the main cabin; install the "outbound" one in the lazarette or similar area. This will cause a constant, gentle current of air to flow through the boat and help not only keep everything dry inside the boat, but also help prevent an accumulation of vapors.

I also have read of people attaching a duct to the aft fan and leading the duct down into the bilge. This setup is even better - you get a flow of fresh outside air coming into the cabin, and then being directed down into the bilge and ducted up and out the aft end of the boat.

Just as a little data point, my boat is a 1968 and has an Atomic 4 in it since new, and the exhaust duct ends just behind the engine - i.e., not all the way down in the bilge. Evidently, it hasn't been a problem yet. Not to make light of the possibility, but is it possible that your concern of having sufficient gasoline vapors in the bilge to cause an explosion may be greater than necessary? Assuming, that is, that the fuel line and associated fittings are in good condition and working order and well-maintained...

[ILikeRust]

We've got two identical threads going on this question.

[snook91901]

Yep, the dual threads are my fault. I wasn't aware of the posting lag for the moderator. I'm going to continue the discussion on this thread if at all possible.

[Administrator]

Threads merged.

Bill

[sailbristol]

i have 3 ducts in my bristol one forward facing intake that terminates above the engine one aft faceing that ends a little below the engine ,and one with a blower attached the ends down in the bilge 3ft below the engine

[edwardc]

...I'm afraid the typical set up with the intake under the engine leading to a blower fan and aft facing exhaust cowl will not work with my boat because the engine compartment is open to the bilge beneath....

My 70's era Pearson was the same way. One of the recommendations that the surveyor made was to extend the blower pickup hose to the lowest part of the bilge.

[sastanley]

My 70's era Pearson was the same way. One of the recommendations that the surveyor made was to extend the blower pickup hose to the lowest part of the bilge.

Last spring, I picked up some blower hose and did exactly this same thing myself. My engine is in the middle of the boat and the hose stopped aft of the companionway steps..I extended it to just in front of the flywheel, which is in the middle of the bilge on my boat, so it is getting the fumes out tout suite!

Welcome to the new guy, too!

[gfatula]

Blower Location?

I am considering moving my squirrel cage blower to make room for a relocated battery. The blower is currently in the space under the quarter birth directly in line with the engine.( the deepest and widest spot) The intake is directly behind and below the engine. That isn't my concern.

How much would it affect the cfm being moved from the intake to the discharge if the location of the blower along that route is changed?

Now a 2' intake run and a 10' run to discharge. I would increase the intake run by 4' and shorten the discharge by the same amount if I relocated the blower to the aft end of the space under the quarter birth. It would seem that with the total run being the same the volume of air getting moved wouldn't change?

In the current location the blower clutters up some valuable real estate.

George

[TomG]

How much would it affect the cfm being moved from the intake to the discharge if the location of the blower along that route is changed?

Without going into Boyle's or Bernoulli's territory too far, the effect on total cfm moved would be negligible given the distances invovled. You are most likely affected more by voltage drop to the blower than anything else, including friction within the duct hose itself.

Move that puppy to less valuable real estate!